According to Cornell, it was a scientist on board the ship who got excited upon spotting the crystal-clear formation.

The white-capped icebergs that are exposed to air appear snowy, while the bottoms of the ice chunks are a vibrant blue. This is due to the way light bounces off the iceberg—when long wavelengths of light (these are red) hit the ice, they are absorbed. In return, the light that makes its way through the ice or bounces off of it is blue.